This invention generally relates to intravascular balloon catheters for procedures such as percutaneous coronary transluminal angioplasty, (PTCA), and particularly to a balloon catheter for deploying stents in conjunction with such procedures.
Typical coronary angioplasty includes advancing a balloon catheter into a patient's coronary artery where the balloon on the catheter is positioned within the stenotic or diseased region of the patient's artery to open up the arterial passageway and thereby increase the blood flow there through. The balloon is inflated with a radiopaque liquid such as a mixture of Renograffin and saline to facilitate fluoroscopic observation of the balloon to ensure properly placement and inflation within the stenosis. After inflation, the balloon on the catheter is deflated and the catheter withdrawn from the diseased arterial region or advanced further into the patient's vasculature for additional treatments or diagnosis.
Very frequently angioplasty procedures include the placement of a stent either during or after the angioplasty procedure to maintain long term patency of the arterial lumen. The balloon catheters used for stent delivery are quite similar to those employed for balloon angioplasty. The balloons on the stent delivery catheters are inflated to expand the constricted stent mounted on the balloon against the vessel wall at the stenotic site. The expanded stent remains at the site and the delivery catheter may be withdrawn after the balloon is deflated.
The mechanical properties of non-compliant or semi-compliant balloons designed for vessel dilatation and/or stent deployment have improved over the years allowing for the use of thinner balloon walls and concomitant lower overall profiles. However, the non-compliant or semi-compliant balloons form wings when in the deflated condition and these wings need to be wrapped tightly around the inner tubular member which extends through the interior of the balloon to present an acceptable profile for advancement through the patient's coronary anatomy. The wrapped balloon may be covered with a protective sheath for storage and transport. The stent may be crimped onto an elastic sheath surrounding the balloon to facilitate a more uniform expansion of the stent. The wings of the balloon are usually heat set in a wrapped condition so they have a tendency to return to the wrapped state upon deflation.
The radiopaque materials (Renograffin) in the inflation fluid used to inflate the balloon, whether for dilatation or stent deployment, are quite expensive, and the viscosity of the inflation fluid is very high, resulting in very slow balloon inflation and deflation times compared with a saline solution not containing radiopaque materials. Efforts in the past to make the balloons on intravascular catheters radiopaque to enable the use of a less viscous non-radiopaque saline solutions have not met with much success. Incorporation of radiopaque materials into the balloon wall usually resulted in unacceptably poor mechanical properties. Coating the balloon with a radiopaque layer usually interfered with balloon folding after inflation and deflation thereof.
Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand to the point of damaging the artery wall.
If the balloon on a dilatation catheter or stent delivery catheter is not properly placed during a dilatation or stent delivery, the inflation of the balloon and stent against the vessel wall may cause damage to the adjacent arterial regions which are not diseased. Placement of the balloon at the stenotic site is frequently difficult because the balloon itself is not radiopaque, so the operator does not have the precise locations of the balloon, the working length of the balloon and the stent. Radiopaque markers on the inner member of the catheter shaft aid in stent placement but the location of the markers are not a guarantee of the location of the balloon and the stent within the stenosis.
Therefore, what has been needed is a catheter balloon with improved fluoroscopic visibility. The present invention satisfies these and other needs.